Electrical circuits often include capacitors for various purposes such as filtering, bypassing, power decoupling, and performing other functions. High-speed digital integrated circuits such as processors and computer chipsets in particular exhibit improved performance when the power supplied to the integrated circuit is filtered with a capacitor placed physically close to the integrated circuit.
Such power decoupling capacitors function to smooth out irregularities in the voltage supplied to the integrated circuits, and so serve to provide the integrated circuits with a more ideal voltage supply.
By placing the decoupling capacitors near the integrated circuit, parasitic impedances such as printed circuit board path resistance or inductance are minimized, which allows easy and efficient transfer of energy from the decoupling capacitor to the integrated circuit. Minimization of series resistance and inductance in the capacitor itself is also desirable for the same purposes, and it results in a more efficient and desirable decoupling or bypass capacitor.
The internal series resistance of the capacitor is typically known as the Equivalent Series Resistance, or ESR. Similarly, internal series inductance is known as Equivalent Series Inductance, or ESL. Both of these parameters can be measured for a given capacitor, and they are among the basic criteria used to select capacitors for applications such as integrated circuit power supply decoupling.
Efforts to minimize ESL and ESR have included solutions such as using multiple types of capacitors in various configurations.